Fibrosis can occur in the lung, liver, kidney, eye, heart, and other major organs of the body. Fibrosis can be due to toxic or infectious injury, such as cigarette smoke to the lungs or viral hepatitis infection of the liver. The cause of some fibrotic diseases is unknown, which is the case with idiopathic pulmonary fibrosis.
Idiopathic pulmonary fibrosis (IPF) is a chronic and insidious inflammatory disease of the lung that kills most of its victims within five years after diagnosis. IPF afflicts 83,000 Americans and more than 31,000 new cases develop each year. It is believed that death due to IPF is greatly underreported and the considerable morbidity of IPF is not recognized. IPF represents just one of the many fibrotic diseases that occurs as a result of chronic inflammation. It is estimated by the United States government that 45% of all deaths in the U.S. can be attributed to fibrotic disorders, and therapeutic agents are needed for treating this condition, especially fibrotic disease of the lungs.
Pulmonary fibrosis leads to progressive scarring and lung destruction. Currently, there are five million people worldwide that are affected by pulmonary fibrosis with 50% mortality at 5 years after diagnosis (Katzenstein A and Meyers Am. J. Respir. Crit. Care Med. 1998, 157, 130-1-15 and American Thoracic Society, Am. J, Respir. Care Med. 2000, 161, 646, 664.). Pulmonary fibrosis is believed to be initiated by insult to the lung parenchyma (either acute or chronic) and develop in patients unable to effectively heal the damage (Gross T. J. N. Eng. J Med 345, 517, 2001). The fibrosis is refractory to corticosteroids and no effective therapy currently exists.
Random screening of molecules for possible activity as therapeutic agents has occurred for many years and resulted in a number of important drug discoveries. While advances in molecular biology and computational chemistry have led to increased interest in what has been termed “rational drug design”, such techniques have not proven as fast or reliable as initially predicted. Thus, in recent years there has been a renewed interest and return to random drug screening. To this end, particular strides having been made in new technologies based on the development of combinatorial chemistry libraries, and the screening of such libraries in search for biologically active members.
In general, combinatorial chemistry libraries are simply a collection of molecules. Such libraries vary by the chemical species within the library, as well as the methods employed to both generate the library members and identify which members interact with biological targets of interest. While this field is still young, methods for generating and screening libraries have already become quite diverse and sophisticated. For example, a recent review of various combinatorial chemical libraries has identified a number of such techniques (Dolle, J. Com. Chem., 2(3): 383-433, 2000), including the use of both tagged and untagged library members (Janda, Proc. Natl. Acad. Sci. USA 91:10779-10785, 1994).
Initially, combinatorial chemistry libraries were generally limited to members of peptide or nucleotide origin. To this end, the techniques of Houghten et al. illustrate an example of what is termed a “dual-defined iterative” method to assemble soluble combinatorial peptide libraries via split synthesis techniques (Nature (London) 354:84-86, 1991; Biotechniques 13:412-421, 1992; Bioorg. Med. Chem. Lett. 3:405-412, 1993). By this technique, soluble peptide libraries containing tens of millions of members have been obtained. Such libraries have been shown to be effective in the identification of opioid peptides, such as methionine- and leucine-enkephalin (Dolley and Houghten, Life Sci. 52, 1509-1517, 1993), and N-acylated peptide library has been used to identify acetalins, which are potent opioid antagonists (Dooley et al., Proc. Natl. Acad. Sci. USA 90:10811-10815, 1993). More recently, an all D-amino acid opioid peptide library has been constructed and screened for analgesic activity against the mu (“μ”) opioid receptor (Dooley et al., Science 266:2019-2022, 1994).
While combinatorial libraries containing members of peptide and nucleotide origin are of significant value, there is still a need in the art for libraries containing members of different origin. For example, traditional peptide libraries to a large extent merely vary the amino acid sequence to generate library members. While it is well recognized that the secondary structures of peptides are important to biological activity, such peptide libraries do not impart a constrained secondary structure to its library members.
To this end, some researchers have cyclized peptides with disulfide bridges in an attempt to provide a more constrained secondary structure (Tumelty et al., J. Chem. Soc. 1067-68, 1994; Eichler et al., Peptide Res. 7:300-306, 1994). However, such cyclized peptides are generally still quite flexible and are poorly bioavailable, and thus have met with only limited success.
More recently, non-peptide compounds have been developed which more closely mimic the secondary structure of reverse-turns found in biologically active proteins or peptides. For example, U.S. Pat. No. 5,440,013 to Kahn and published PCT WO94/03494, PCT WO01/00210A1, and PCT WO01/16135A2 to Kahn disclose conformationally constrained, non-peptidic compounds, which mimic the three-dimensional structure of reverse-turns.
While significant advances have been made in the synthesis and identification of conformationally constrained, reverse-turn mimetics, there remains a need in the art for small molecules, which mimic the secondary structure of peptides. There has been also a need in the art for libraries containing such members, as well as techniques for synthesizing and screening the library members against targets of interest, particularly biological targets, to identify bioactive library members. For example, U.S. Pat. No. 5,929,237 and its continuation-in-part U.S. Pat. No. 6,013,458 to Kahn also discloses conformationally constrained compounds which mimic the secondary structure of reverse-turn regions of biologically active peptides and proteins. The synthesis and identification of conformationally constrained α-helix mimetics and their application to diseases are discussed in Walensky, L. D. et al Science 305, 1466, 2004; Klein, C. Br. J. Cancer. 91:1415, 2004.
Many models of pulmonary fibrosis have been developed, however regardless of the nature of the initial insult the stages of progression appear to be quite similar. A generally accepted model involves damage to the endothelial and type I alveolar epithelial cells followed by interstitial edema, deposition of fibrous materials in the alveolus in areas of loss of type I epithelial cells. It is believed that limited proliferation of the type II cells and subsequent differentiation into type I and Clara cells is critical to reestablishment of normal gas exchange.
Anti-inflammatory therapies (e.g. corticosteroids, interferon-γ) to treat pulmonary fibrosis have been disappointing to date due to limited efficacy and severe adverse side effects. An important unmet need exists to identify the key molecular pathways involved in the development and progression of pulmonary fibrotic diseases and to develop new therapeutic agents to prevent the progression and reverse the disease process. No drugs have been approved for the treatment of any fibrotic disease in the United States. Research and development is desperately needed to provide treatments to those afflicted with fibroproliferative diseases. The present invention fulfills these needs, and provides further related advantages by providing conformationally constrained compounds which mimic the secondary structure of α-helix regions of biologically active peptides and proteins.